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Proceedings of the American Academy of Arts and Sciences. 


Vou. 58. No. 1.—Frsruary, 1923. 


VISION AND THE TECHNIQUE OF ART. 


By A. Ames, Jr., C. A. Proctor anp BLANCHE AMES, 


INVESTIGATIONS ON LicHT AND HEAT, PUBLISHED WITH AID FROM THE 
RumMrorp Funpb. 


w 


VISION AND THE TECHNIQUE OF ART. 


By A. Amms, Jr., C. A. PRocrork AND BLANCHE AMES. 


Presented by Louis Bell. 
Received Jan. 20, 1922. Presented Jan. 11, 1922. 


INTRODUCTORY. 


THERE are many well known instances where very successful use has 
been made by artists of certain of the laws of vision as a basis of 
technique. The “pointillist”’ technique of Pissaro and Monet is 
probably the best example. 

The artist Birge Harrison! has gone farthest towards recognizing 
the dependency of the technique of art on the laws of vision. He 
most forcefully and lucidly shows that a picture in its general form 
should be similar to our retinal impressions. Mr. Ames and his sister, 
Blanche Ames, who were painting together came to a similar con- 
viction in 1912. Attempts were made to paint pictures of this 
nature. The difficulty of analyzing the character of images of objects 
upon which the eye was not focused was at once encountered. This is 
without doubt due to the universal and probably immemorial human 
practice of looking directly at, i.e., focusing upon anything we desire 
to judge or analyze. Mr. Ames therefore undertook to determine 
scientifically the characteristics of the images of those objects upon 
which the eye is not focused in the belief that an intellectual concep- 
tion of the characteristics of such images would help in the visual 
recognition and analysis of them, and thus be an aid in the technique 
of art. 

He thought that the desired information could be obtained in a few 
weeks — at most afew months. The scientific data upon which such 
information is based, however, had not been worked out. This 
necessitated research work upon which he has been occupied up ‘to 
the present. The data collected, although representing a consider- 
able advance, constitute hardly more than the preliminary steps 
towards definitely determining the characteristics of the retinal 


1 “Landscape Painting” by Birge Harrison. Charles Scribner’s Sons. 


4 AMES, PROCTOR AND AMES. 


picture. Most of the data has been published in a paper by Mr. 
Ames and Dr. C. A. Proctor, entitled “ Dioptrics of the Eye.” 2 

It is the purpose of the present paper to convey as clear an under- 
standing as possible of the nature of the retinal picture and to point 
out conclusions to which such an understanding leads us. 


PREFACE. 


A consideration of the analogy between our eye and a photographic 
camera is helpful for a general understanding of the subject. 

Broadly speaking the eye is like a camera, or more truly speaking 
cameras were made like the eye, the lens of the camera corresponding 
to the lens of the eye and the plate or film to the retina. As the 
character of a photograph depends upon the kind of lens and plate 
used, so the characteristics of our retinal picture depend first upon the 
nature of the lens of the eye and second upon the nature and sensi- 
tivity of the nerve structure, i.e., the retina upon which the image is 
formed. ° 

Certain photographic lenses are corrected. The detail in photo- 
graphs taken with such lenses is clear and distinct over the entire 
picture and free from distortion. Other photographic lenses which are 
not corrected produce pictures in which the detail is indistinct and 
distorted in varying degrees. 

The lens system of the eye is not corrected. The details in part of 
the image formed by it are clear, in other parts unclear and all more or 
less distorted. 

Furthermore, the retina, instead of being equally sensitive over its 
entire area as 1s a photographic plate, varies in sensitiveness in differ- 
ent parts. 

As a result of the effects of the lens system of the eye and the effects 
of the variable sensitivity of the retina the retinal picture has charac- 
teristics which make it markedly different from photographs taken 


2 Journal Opt. Soc. of Amer., Vol. V, Jan. 1921. 

3 The image of a scene formed by a simple lens (called uncorrected), such as 
a spectacle lens or a magnifying glass, is not an exact reproduction of the scene 
itself. The detail of objects at the center of the picture is slightly softened and 
has chromatic edges. The detail at the sides of the picture is still more softened 
and objects at the side are bent and distorted. 

To make the detail at the center as well as at the sides perfectly sharp and 
to do away with distortion, so called corrected lenses were devised. They 
consist of a combination of two or more simple lenses of determined character 
and separation. 


VISION AND THE TECHNIQUE OF ART. 5 


with a corrected lens or even with an uncorrected lens. For though the 
eye has an uncorrected lens, the lack of corrections, so to speak, is 
markedly different from that existing in any known uncorrected 
photographic lens, and so produces a different effect. 

To give an understanding of the more specific characteristics of the 
retinal picture it is necessary to take up and describe the character- 
istics of the images formed of objects in different parts of the field of 
view, 1.e., the scene at which we are looking. 

We shall take up the images of objects in the various parts of the 
field of view in the following order: First, the images of objects at’ 
which the eye is directly looking, or, in other words, those objects 
which lie in the line of vision and which are in sharp focus. See A, 
Figure 1. This will be covered in Chapter I, Distinct Vision. 


Figure 1. Diagram showing positions of various objects in the field of 
view. KF BA Cis the axes of vision or line of sight along which the eye is 
looking. A is the object on which the eye is focused. It will be imaged 
sharply on the fovea F. B and C are points on the line of sight inside and 
outside the point of focus. D is an object to one side of the line of sight. It 
will be imaged on the peripheral part of the retina at G. 


Second, the images of objects which are on the line of vision nearer 
and farther away than the object in focus (see B and C, Figure 1); 
Chapter II, Depth of Field Axial. 

Third, the images of objects which are not in the direct line of vision 
as D, Figure 1. These images will be described in Chapters III, IV 
and V. 

Chapter III, Depth of Field (Lateral), will deal, with the character- 
istic imaging of objects not in the direct line of vision and at different 
distances from the eye. See D and H, Figure 1. 

Chapter IV, Distortion in Form, will deal with the distortion of the 
images of objects not in the direct line of vision. 

Chapter V, Peripheral Color Sensitivity, will deal with ‘the change 
in the local color of images of objects not in the direct line of vision. 

In Chapter VI the effect of binocular vision will be considered in a 
general way. 

In Chapter VII the results will be summarized and discussed. 


6 AMES, PROCTOR AND AMES. 


CHAPTER I. 


DISTINCT VISION. 


Distinct vision deals with the nature of retinal images of objects at 
which the eye is looking directly, 1.e., that are in sharp focus. As we 
have a very definite conception of the appearance of objects at which 
we look directly it may hardly seem necessary to analyze the char- 
acteristics of the images of such objects. It is believed however that 
such an analysis will not only be instructive but will make it easier to 
understand the characteristics of the images of objects upon which the 
eye is not focused, which will be taken up later. 

Owing to the nature of the lens system of the eye the image on the 
retina formed by an object at which the eye is directly looking is not 
an exact copy of the object itself. Theimage is spread out and some- 
what diffused. This is due primarily to three factors; chromatic aber- 
ration; spherical aberration; and irregular astigmatism. These factors 
and their effects will be considered in the order given. 


CHROMATIC ABERRATION. 


Chromatic aberration causes light of different wave length or color 
to come to focus at different distances behind the lens, light of shorter 
wave length, 1.e., towards the blue end of the spectrum focusing 
nearer the lens. This is shown in Figure 2. 


Figure 2. Diagram showing chromatic aberration of the eye. 


If we have three point sources of light at A, one red, one yellow, and 
one blue, the image of the blue source will be formed at (b) the image 
of the yellow source at (y), while the red image will be at (r). Figure 
3 shows the shape of image bundles as formed in Mr. Ames’ eye by 
point sources of red, yellow and blue light. These of course are much 
enlarged; the lens system of the eye is to the left. 

It will be seen that the blue bundle lies to the left or nearer the lens 


VISION AND THE TECHNIQUE OF ART. q 


than the yellow bundle and that the yellow bundle lies to the left of 
the red. 

The eye normally focuses for yellow light, i.e., so that the small 
cross section of the yellow bundle falls on the retina. If the eye looks 
at red, yellow, and blue point sources at the same time the retina 
would be in the position relative to the three bundles as shown in 
Figure 3. It will be noted that the smallest cross section of the blue 
bundle lies in front of the retina, that of the red behind. 


R 
—Olm m., e 
Scale. v 
= ——— = Axis Red 
= 
: SS B Axis Yellow 
—————— 
[ee Axs Burue. 


Figure 3. Image bundles formed by light from red, yellow, and blue point 
sources. ‘Their displacement right and left shows the Chromatic Aberration 
of the eye. The different distances from the retina at which the individual 
rays, in each bundle, cut the axis shows the Spherical Aberration. 


It will also be noted that where the red and blue bundles cut the 
retina they are much larger in diameter than the yellow bundle. This 
is also shown in Figure 4 which is a photograph of the magnified image 
of a point source of white light taken with a lens which has approxi- 
mately the same chromatic aberration as the eye. A white light source 
is composed of light of all wave lengths. The camera was focused to 


8 AMES, PROCTOR AND AMES. 


get as sharp an image as possible of the yellow light and then the three 
pictures were taken, the top one through a red screen, the middle one 
through a yellow,* the lower one through a blue. The top photo- 
graph therefore shows the image formed by the red rays in the white 
light source, the middle one that formed by the yellow rays, and the 
bottom one that formed by the blue rays. 

Colored images of the same relative difference in size are apparent 
to the eye looking at a point source through monochromatic screens or 
filters if the eye is kept focused for yellow. Without any screens or 
filters the eye receives an image of the nature obtained by combining 
the three images in Figure 4. It would have a bright center tending 
towards yellow in color, surrounded by larger and larger rings of 
shorter and longer wave lengths, the blue rings extending out farther 
than the red. 

A comparison of the image formed by the eye and that formed by a 
lens corrected for chromatic aberration is of interest. Such a lens is 
designed so that light of all wave lengths focuses at the same distance 
from the lens. This is shown in Figure 5 where it will be seen that the 
narrowest part of the bundles for light of different wave length, in- 
stead of being focused at different distances from the lens, all focus at 
the same distance. Figure 6 is a photograph of a point source of white 
light taken with a corrected lens. The photographs were made in the 
same way as those in Figure 4. It will be noticed that where the 
images taken through the red, yellow and blue screens with the un- 
corrected lens are all of different size similar images formed by a cor- 
rected lens are substantially all the same size. That is, this correction 
causes the images of an object in focus to be much sharper or clearer 
than those formed in the eye. 

We have been speaking so far only of point source objects. If the 
object is either a line or an edge, for instance a dark edge of a window 
against a light sky, the diffusion circles we have been describing take 
the form of diffusion edges. The distribution of color in these diffu- 
sion edges follows the same laws as govern that in the diffusion circles. 
This is shown clearly in Figure 7, which is a photograph taken through 
a lens having approximately the same chromatic aberration as the eye, 


4 As the filters actually used in taking this and following pictures were East- 
man Kodak Co. films Red No. 25, Green No. 58 and Blue No. 48, it would be 
more exact to use the word “green” instead of “‘yellow.”’ The difference in 
wave length between the green and yellow however is such that there would be 
no appreciable differences in the appearance of the photographs whether a 
green or yellow filter was used. The term yellow will therefore be used for 
sake of simplicity and clearness. 


RED. 


RED. 
YELLOW. 
YELLOW. 
BE: BLUE. 
Fig. 4. Fig. 6. 


Plate or Screen 


Arnis Red _ 


Axi 3 Yellow. 


Hig; 


Figure 4. Three color photograph of a white light point source taken with 


lens having same chromatic aberration as the eye. Magnification 110 diame- 


ters. 
Figure. 5. Image bundles which would be formed by light from red, yellow 


and blue point sources passing through a lens perfectly corrected for chromatic 


and spherical aberration. ; } : ; 
Figure 6. Three color photograph of a white light point source with a 


lens corrected for chromatic aberration. Magnification 110 diameters. 


RED. 


YELLOW. 


BLUE. 


Fig. 7. Fig. 8. 


Fiaure 7. Three color photograph of black and white wedges taken with 
lens having the same chromatic aberration as the eye. The base of the 
wedges which were about six feet distant measured } inch. 

Fiaure 8. Same as Figure 7 taken with a lens corrected for chromatic 
aberration. 


VISION AND THE TECHNIQUE OF ART. 9 


of a white wedge on a black background and a black wedge on a white 
background. The base of the wedges was one-fourth inch and their 
distance six feet from the camera. 

The top picture was taken through a red, the middle through a 
yellow, and the bottom one through a blue filter. The camera was 
focused to give a sharp image with the yellow filter. The top picture 
shows the kind of image that is formed on the retina by the red light, 
the middle one the kind of image that is formed by the yellow light and 
the bottom one the kind of image that is formed by the blue light. If 
you imagine these superimposed, which is what takes place on the 
retina, the combined picture will have a blue diffused edge extending 
over the black and a less wide red edge. The color of the white near 
the edges will be slightly yellowish due to the subtraction of the blue 
and red. 

With a lens free from chromatic aberration no such effect is pro- 
duced. ‘This is shown by Figure 8, which is a photograph of the same 
objects taken at the same distance and in the same way, with a cor- 
rected lens. ‘The images of all the wedges in this case are sharp and 
clear and of the same size. They will all exactly superimpose and no 
chromatic edges will be formed. 

Under ordinary circumstances unless the attention is especially 
called to them these chromatic rings and edges formed in the eye are 
not seen. ‘This is due, it is believed, partly to the fact that the red 
rings overlie the green, which being complementary colors form white 
light, and to the fact that the blue is so spread out that it is relatively 
weak. However, if one looks carefully for these rings or edges they 
can be seen around an arc light at night, in the blue haze or halo on the 
dark background. 

The red and blue chromatic circles or edges can be seen separately 
by looking at a dark object, such as a window sash against a bright sky 
at a distance of three to six feet and shutting off the light from half the 
pupil by passing a card or piece of paper close to the eye, the edge of 
the paper being kept parallel to the window sash. One side of the 
frame will have a red orange edge, the other a bluish edge. If the 
card is brought in from the other direction the color of the edges will 
reverse. Without the card the colors overlie each other and become 
much less visible for the reason given above. However, once the 
phenomenon has been noticed a soft floating purplish edge becomes 
apparent even without the card. : 

A very striking example of chromatic aberration, and one which 
gives a very good idea of its magnitude, is apparent when one looks 


10 AMES, PROCTOR AND AMES. 


at the purple railroad switch lamps used, for example, by the Boston 
and Albany Railroad. At close range these lamps appear purple, 
but as one moves away the light appears to have a red center sur- 
rounded by a blue disk or halo; the farther off one goes the larger 
the blue halo appears. 


SPHERICAL ABERRATION. 


Another factor that has a bearing on the nature of the retinal image 
of an object on which the eye is focused is the spherical aberration 
mentioned above. In a lens free from spherical aberration the rays 
that come through different zones of the lens, for example those that 
come through the lens near its center and near its edge, all focus down 
to a point. This is shown in Figure 5 where rays near the outside of 
the cone and those near its center all go through one point at the apex 
of the cone. In a lens which has spherical aberration this is not true. 
_ The rays from different zones of the lens do not pass through the same 
point. This is shown in Figure 3, where it will be seen that ray A, for 
instance, crosses the axis far to the left of ray B. Due to this fact the 
image of a point source formed in the eye will be larger ae with softer 
edges than that formed by a corrected lens. 


IRREGULAR ASTIGMATISM. 


There is still another factor that has a bearing on the nature of 
retinal images of an object on which the eye is focused. That is 
irregular astigmatism. This term covers all irregularities in the shape 
and distribution of light in the image due to such things as opaque 
substances or irregularities of densities in the lens system. A most 
marked example of this factor is the star shape appearance, known to 
everyone, of a small source of light. If the eye were not subject to 
irregular astigmatism of some sort the image of a small source, though 
‘it might be affected by chromatic and spherical aberration, would be 
circular. Such retinal images, however, are always star shaped. 


SUMMARY. 


The three aforementioned factors, chromatic aberration, spherical 
aberration, and irregular astigmatism, cause the retinal image of an. 
object upon which the eye is focused to have a characteristic appear- 
ance both as to the amount of detail which is visible and in the appear- 
ance of all edges. 


VISION AND THE TECHNIQUE OF ART. 11 


From the point of view of the technique of art the question arises is 
it necessary that these characteristics be reproduced in the depicting 
of an object upon which the eye is focused? 

The care used by the better artists to paint broadly, 1.e., not to get, 
even in the most detailed parts of their pictures, any more detail than 
is apparent to them at the distance at which they stand from their 
model or scene and their quite common practice of softening and treat- 
ing their edges, is evidence that to be technically satisfactory from an 
artistic point of view the detail of an object on which the eye is focused 
should be depicted with the same characteristics with which it is 
imaged upon the retina. This evidence is further supported by the 
fact, as will be shown later, that the characteristics of the images of 
objects upon which the eye is not focused, must be reproduced to 
bring out the appearance of depth and to make the pictures pleasing. 


CHAPTER II. 
DEPTH OF FIELD (AXIAL). 


In this chapter we will deal with the nature of images of objects that 
are in the line of vision nearer and farther away from the observer than 
the object upon which the eye is focused. 

The images of such objects will have markedly different charac- 
teristics from those of objects in focus. 

These characteristic differences are due primarily to two factors. 
First, Depth of Field of the lens system; second, Chromatic Aberra- 
tion. : 


Figure 9. Diagram showing diffusion of images of point source objects 
not in focus. 


DEPTH OF FIELD. 


For sake of brevity and simplicity a full explanation of Depth of 
Field will not be gone into. It is evident however that an object which 
lies nearer or farther from the observer than the object upon which he 
is focused will be imaged not on the retina but behind it or in front of 
it. This is shown in Figure 9. 


12 AMES, PROCTOR AND AMES. 


The image of point source object A upon which the eye is focused is 
imaged on the retina at (a), that of B behind the retina at (b), that of 
C in front of the retina at (c). Where the image bundle which forms 
the image (b) cuts the retina it is a cone of considerable size. The 
object B will appear as a diffusion circle. The image bundle which 
focuses down to the image C in front of the retina is spread out again 
and also appears as a diffusion circle. If instead of a point source the 
objects at B and C are objects with edges the edges will have the well 
known appearance that is seen on an object that is out of focus, i.e., 
a pencil held near the eye while the eye is focused on a distant object. 
The nearer the objects B and C approach A the smaller will be the 
size of these diffusion circles and the more similar all their images be- 
come. The magnitude of this effect depends upon the focal length of 
the lens system and the size of the aperture. In the eye this means, 
broadly speaking, the length of the eye and the size of the pupil. It 
is very marked where either the objects in or out of focus are close to 
the eye but decreases as they are moved away and becomes im- 
perceptible when they all are at a distance of thirty feet or more. 


CHROMATIC ABERRATION. 


As was described in Chapter I the effect of chromatic aberration is 
to cause light of different wave length or color to focus at different 
distances from the lens. See Figure 2. 

If we move the blue point source at A, Figure 2, towards the eye, 
the eye being kept focused on A, it will cause the image of the blue 
source to move back towards the retina. <A position B, Figure 10, 
will be found where a blue light will focus'sharply on the retina while 
the eye is still focused on the point at A. If we move the red light 
away from the eye a similar position R, Figure 10, will be found where 
the red light will also be in focus. 


Ficure 10. Diagram showing how images from sources of different colors 
situated at different distances from the eye can all be in focus at the same time. 


That is all three lights will be in focus at the same time although 
they are at very different distances from the eye. For example if the 
eye is focused on a yellow light at a distance of six feet it will see 


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VISION AND THE TECHNIQUE OF ART. 13 


sharply at the same time a blue light about three feet away and a red 
light at about twenty feet away. 

We described in Chapter I the characteristic chromatic diffusion 
circles and edges of an object in focus. We saw that a white light 
point source as at A, Figure 10, would form an image with a yellowish 
center surrounded by red and blue diffusion circles. A white light 
point source at B, Figure 10, however, will form quite a different image. 
The blue in the white light being in focus will, as we have just shown, 
form asharpimage. ‘The yellow will be out of focus and form a yellow 
diffusion circle around the blue and the red will be still more out of 
focus and form a larger red diffusion circle which will extend outside 
that of the yellow. 

Figure 11, is a photograph of a point source of white light taken with 
a lens which has approximately the same chromatic aberration as the 
eye. The lens was focused to give a sharp image of the yellow rays in a 
white light source about six feet away. The pictures are of a white 
light point source about three feet away. As in Figure 4 the top 
image was taken through a red, the middle one through a yellow, and 
the bottom one through a blue filter. The combined image which is 
the appearance the white light point source would have to the eye is 
markedly different from that shown in Figure 4. 

A white light point source at R, Figure 10, will form a still different 
kind of image. ‘The red in the white light being in focus will form a 
sharp image. The yellow will be out of focus and form a yellow 
diffusion circle around the red and the blue being still more out of 
focus will form a larger blue diffusion circle. 

Figure 12 is a photograph similar to those described in Figure 4 and 
Figure 11, but with the objects twenty feet away. The images 
formed are very different from those shown in Figure 4 and 11. 

Images of white light point sources situated at other distances along 
the axis will vary from those shown above, their characteristics de- 
pending on the position of the fixation point and their distance from it. 

A lens corrected for chromatic aberration forms very different 
images of similar white light point sources. Figures 13 and 14 are 
photographs taken with a corrected lens. The photographs were 
made in the same way as those shown in Figures 11 and 12 of white 
light point sources in similar positions. As the point in the focus of a 
corrected lens is in focus for all colors so a point out of focus is out of 
focus for all colors and to the same extent. The diffusion circles for 
red, yellow and blue light in Figures 13 and 14 are therefore all about 
the same size. The combined image although enlarged and fuzzy will 


14 AMES, PROCTOR AND AMES. 


appear white, i.e., without colored edges, no matter in what direction 
or distance the white light point source is from the point in focus. 

As described in Chapter I if instead of a point source edges are used, 
as a dark object against a light background, the above described 
diffusions make themselves evident in the form of chromatic edges. 

Figure 15 shows a photograph taken with a lens, which has approxi- 
mately the same chromatic aberration as the eye, in the same way and 
of the same objects as described in Figure 7. The lens was focused as 
described for Figure 11 for yellow at six feet, the objects being three 
feet away. ‘The combined images are marked by the orange red edges 
extending over the dark and the blueness of the white along its edges 
due to the subtraction of the red and yellow light which has diffused 
over the black. 

Figure 16 is a similar photograph, the focus of the lens remaining the 
same, the objects being placed at a distance of about twenty feet. In 
this case the combined images are characterized by the green and blue 
extending over the dark and the redness of the white along its edges. 

It is regretted extremely that these pictures cannot be reproduced 
in color as they not only show these characteristics much more clearly, 
but are very beautiful. 

Figure 17 is similar to Figure 15 taken with a corrected lens. As 
would be expected from what has been said of Figures 13 and 14 the 
images taken through the different filters are all diffused to the same 
extent. As a result the composite picture shows diffused but no 
colored edges. 

Once one’s attention has been called to them, these characteristic 
chromatic edges in the retinal images are very easily seen. ‘The 
aberration of the red rays over the dark, characteristic of images of 
objects which lie inside the focus, was first noticed in the warm color 
of black specks on a windowpane viewed from a few feet when the eye 
is focused on the distant sky. All of the characteristic colored edges 
can be easily seen with the following arrangement. Against the white 
wall of a room or a piece of cardboard or sheeting put up at the distance 
of about twenty feet a black object, preferably one that comes down 
to fine black points, as iron grill work, black wedges of paper will do. 
At six feet distance put up any small object to focus on in line with the 
distant objects. At three feet distance in the same line put up another 
black object preferably like the first. If the eye is kept focused on the 
object at six feet the dark edges of the near object appear to have a 
reddish orange tinge next to which the light appears colder or bluer. 
The edges of the object at twenty feet, in fact the whole surface if the 


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7, 


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VISION AND THE TECHNIQUE OF ART. 15 


dark objects are narrow enough, appear very bluish while the lights 
next to the dark objects appear pale orange. Of course if the focus of 
the eye is not kept fixed on the central object these appearances will 
not be visible for they only exist on objects that are not in focus. It 
may take some practice to keep from changing the focus as the natural 
tendency is to focus upon the object which one is trying to analyze. 

The colored edges on both far and near objects are best seen when 
the objects are at the relative distances above described. Red edges 
on the dark become more evident with a more distant fixation and 
blue on the dark with a nearer one. 

Where both the fixation and the nearer object are twenty feet or 
more away both objects are so nearly in the same focus that the 
difference in colored edges is hard to distinguish. 

These facts lead naturally to the assumption that with a given fixa- 
tion the characteristic colored edges of objects nearer and farther than 
the fixation object inform us of their relative distance, that is, if an 
object has red edges we judge it to be nearer to us than the fixation 
object while if it has blue objects we judge it to be farther away. If 
this is so objects depicted in a picture with red edges should appear 
nearer than those with blue edges. This is exactly what was found to 
be the case as is shown by Figure 17a. It will be seen that the circles 
with the reddish edges appear to be on a nearer plane than those with 
the blue edges.® 


SUMMARY. 


The effect of depth of focus which produces the fuzzy edges of objects 
nearer or farther than the object plane has been long recognized in 
photography. 

This is shown in the photographs in Figures 18 and 19. That in 
Figure 18 was taken with a small aperture, F 16, which causes objects 
at all distances to be imaged sharply, while that in Figure 19 was taken 
with a large aperture, F 4.5, which causes objects nearer and farther 
than the focus point to the imaged with a greater softening of edge. 
The greater effect of depth in the photograph in Figure 19 as compared 
with that in Figure 18 is very evident. 

Gleichen ® goes into the subject at length and points out that a. 


5 The illusion is more apparent if one eye is closed. This prevents the 
functioning of our binocular depth perception by which we tend to recognize 
the true distance of both figures. 
' 6 “Die Grundgesetze der naturgetreuen photographischen Abbildung.” 
Halle 1910. ‘‘Uber Helligkeit und Tiefe inbesondere bei der naturgetreuen 
Photographischen Abbildung.”’ Zeit, fur Wiss. Phot. Vol. 9, 1911, p. 241. 


16 AMES, PROCTOR AND AMES. 


natural effect of depth can only be produced by a lens which has the 
same depth of field as the eye. 

He does not, however, deal with the effects of chromatic aberration. 
The depth effect due to it is believed to be much more marked than 
that due to simple depth of field. 

In simple depth of field the diffusion of edge due to an object bein 
out of focus gives no indication as to whether the object is nearer or 
farther than the focus point. Chromatic aberration on the other hand 
causes objects beyond the focus point to be imaged in a characteris- 
tically different way from those inside. This in turn gives a real basis 
for monocular depth perception apart from the relative sizes of 
objects or disappearing or other perspective. As shown by Figure 17a 
this effect of depth can be obtained in a picture if the objects are de- 
picted with their characteristic chromatic edges. A marked effect of 
depth has thus been obtained in pictures painted by Blanche Ames. 

Many paintings by great masters have been looked at to find 
whether this characteristic edging has been made use of. The treating 
of edges as stated before is quite common, and in certain paintings, 
by Millet for instance, warm or reddish edges are found around near 
objects while objects in the distance are colder and bluer. It is not 
felt, however, that the evidence is sufficient to conclude that it has 
been used consistently. 


. CHAPTER III. 


DEPTH OF FIELD (LATERAL). 


In this chapter we will deal with the characteristics of images of 
objects which are situated not on the line of vision. The characteristic 
form of such images is due primarily to an aberration called oblique 
astigmatism. (This should not be confused with corneal astigmatism.) 

Oblique astigmatism causes the rays of light, from a point source 
not on the axis, to focus into a ray bundle of complex form. As ex- 
plained above the ray bundle from a point source on the axis focuses 
_ in the form of a cone to a point where the rays cross to spread out into 
another cone. The ray bundle from a point source not on the axis 
forms a more complicated figure. In its pure form in a simple un- 
corrected lens it focuses first to a line, see aa, Figure 22, which lies in a 
position tangential to a circle about the axis of the lens. It then 
crosses and narrows in its long dimension and lengthens in its short 


I'rcure 18. Photograph taken with a small aperture, i.e. F 16. 


Figure 19. Same view as in Figure 18 taken with a 
large aperture, i.e. F 4.5. 


Ppa 


VISION AND THE TECHNIQUE OF ART. 17 


one until it becomes a line again, see bb, Figure 22, which is perpendicu- 
lar to the first line. . : 

The image of every point source not on the axis has this peculiar 
form. ‘The farther the source from the axis the greater the separation 
between the two parts of the image which have the form of lines. Ifa 
sensitive plate or ground glass screen is placed behind the lens the 
form of the image that is apparent depends upon the position of the 
screen. If it is placed far back, i.e., to the left of bb, Figure 22, the 
image will be in the form of a radial oval, i.e., radial to a circle about 
the axis of vision, in the horizontal plane this would be horizontal; 
if at bb, in the form of a radial line; if half way between aa and bb, 
the form of a circle; if at aa, the form of a tangential line, i.e., tangen- 
tial a circle about to the axis of vision, in the horizontal plan this 
would be vertical; if still nearer the lens, in the form of a tangential 
oval. If the screen is held stationary relative to the lens, a similar 


Figure 22. Diagram showing characteristic shape of the image bundle of 
a point source not on the axis. 


change in form of image can be noted by moving the point source from 
a distance to a position near the lens, always keeping it at the same 
angular obliquity. 

If, instead of a point, a line source is used, a similar imaging takes 
place. Every point on the line source is stretched tangentially or 
radially, depending upon the position of the line source. It can be 
seen that if the stretching of the various parts of the line source is along 
the length of the line source itself, the image of the line will appear 
perfectly sharp and slightly elongated. That is, if a line source is tan- 
- gential to the axis, its image will be sharp when the source is so posi- 
tioned that the part of the image that forms a tangential line, i.e., aa, 
Figure 22, falls on the screen. If it is in a position radial to the axis, 
its image will be sharp when that part of its image that forms a radial 
line falls on the screen. 


18 AMES, PROCTOR AND AMES. 


In all simple lenses this characteristic image formation is more or 
less confused by coma, a one-sided blur, and by chromatic aberrations. 
The magnitude of these aberrations in the eye has not yet been 
measured. 

This may all be madea little clearer by a brief description of how 
Mr. Ames measured the oblique astigmatism in his own eye. A point 
in space is fixated with one eye, i.e., by focusing on a point of light, the 
line of vision and the focus of the eye is not allowed to vary. At one 
side of the line of vision (at an angle of obliquity of five degrees), three 
narrow tangential lines (in this case vertical) of yellow light were 
moved back and forth. It was found that when these lines were at a 
certain distance they could be distinguished as separate. At any other 
distance they could not be distinguished. The distance at which they 
could be distinguished was such as to cause that part of the image 
designated as aa, Figure 22, to fall on the retina which made the tan- 
gential lines appear most sharp. This point was found to be nearer 
than the fixation point. Similar points were found at varying degrees 
of obliquity from the axis where the three narrow lines appeared most 
sharp. In this way a surface in space was determined where yellow 
tangential lines were most visible. The shape of this surface which is 
called the primary astigmatic object field for yellow is shown in plan 
on Figure 23 by the solid lines extending from the Po marked 
“fixation point” back towards the eye. 

In the same way a surface in space was determined when yellow 
radial lines were most visible. This is called the secondary astigmatic 
object field for yellow and is shown in plan by the dotted lines extended 
in shape of a ram’s horns from the point marked “fixation point”’ 
outward. Figure 23. 

Corresponding fields for red, blue and green monochromatic light 
were found and are shown in Figure 23. 

If this fixation point is changed although these primary and second- 
ary astigmatic object fields keep their general shape they shift forward 
and backward. 

Heinrich? made a similar experiment with a black thread. He 
moved a black vertical thread (as he worked in a horizontal plane this _ 
would be a tangential line) which was placed to one side of the line of 
vision, back and forward until it appeared most like the thread on > 
which the eye was fixiated. He found a field similar in shape and 
position to that which the writer found for the primary astigmatic | 
field for yellow. 


7 British Journal of Psych., Vol. 3, p. 66. 


VISION AND THE TECHNIQUE OF ART. 19 


BR es pce ME Cath ei) bt 
re 84 S° to 


4 


Wy 


7 


A 


| 

HT / 

/ up ve 
a ow. 

/ 


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Figure 23. Position of primary and secondary astigmatic object fields for 
different colors. 


20 AMES, PROCTOR AND AMES. 


This means that with any given fixation, at a given angle of obliquity, 
there are certain positions in space where tangential black and white 
lines appear most sharp and other positions where radial black and 
white lines appear most sharp. It also means that with the same 
fixation there are still other positions where tangential lines of a 
particular color will appear most sharp and still other positions where 
radial lines of the same color appear most sharp. The positions in 
space therefore where tangential and radial colored lines appear most 
sharp depend upon their color. 

The different position of the primary and secondary astigmatic 
fields for different colors has a further effect of causing the images of 
black and white objects to have characteristic chromatic edges due to 
their position in space relative to the fixation point. This can be best 
shown by the following photographs taken with a lens which has 
approximately the same oblique astigmatism and chromatic aberration 
as the eye. 

Figure 24 (b) is of a white light point source situated at C, Figure 23, 
1.e., in the secondary field for yellow at an angular obliquity of about 
eighteen or twenty degrees. As the lens is focused at the distance 
marked “fixation point” this is in the plane of the focus. The top 
picture shows the image formed by the red rays in the white light 
source; the middle that formed by the yellow; the bottom one that 
formed by the blue. As the point source is in the secondary field for 
yellow the yellow light is stretched in a radial.direction. Being near 
the primary field for red the red is beginning to be stretched in a 
tangential direction. And being beyond the secondary field for blue 
the blue is stretched in a radial direction forming a diffused radial oval. 

Figure 24 (a) is a photograph of a white light point source situated 
at B; Figure 23, 1.e., in the secondary astigmatic field of red light. 
The red light is therefore stretched in a radial direction. The point 
source being beyond the secondary fields for both yellow and blue 
light they are imaged as diffused radial ovals, the blue more diffused 
than the yellow. 

Figure 24 (c) is of a white light point source situated at D, Figure 23, 
1.e., near the primary field of red and yellow and the secondary of blue, 
consequently we see the red and yellow stretched in a tangential 
direction, the blue in a radial one. 

The images of white light point sources in similar positions forned 
by a lens corrected for oblique astigmatism and chromatic aberration 
are quite different. Figure 24 (e) is such a photograph of a white light 
point source at C, Figure 23, i.e., in the plane of the focus. The lens 


RED. 


YELLOW. 


BLUE. 


(a) 


RED. 


YELLOW. 


BLUE. 


(d) (e) 


Figure 24. Three color photographs showing characteristic image forms 
of white light point sources at different distances. (a) (b) and (c) were taken 
with a lens having approximately the same chromatic aberration and astigma- 
tism as the eye. (d) (e) and (f) were taken with the sources at the same dis- 
tances with a corrected lens. Magnification 28 diameters. 


VISION AND THE TECHNIQUE OF ART. yal 


being corrected for oblique astigmatism means that the image lines aa 
and bb, Figure 22, are brought together to a point on the image plane. 
There is therefore none of the characteristic stretching in tangential 
and radial directions which was so evident in the oblique images 
formed by the other lens. The lens also being corrected for chromatic 
aberration there is no substantial difference in the form of the images 
for the different colors. They are all imaged as small spots of light 
of about the same size. The marked difference in imaging from that 
which occurs in the eye as shown in Figure 24 (b) should be noted. 

Figure 24 (d) and (f) are photographs made with a corrected lens of 
white light point sources at B and D, Figure 23. Due to the correc- 
tions the images do not show any stretching in a radial or tangential 
direction and they are all the same shape and size for different colors. 
The combined images will therefore appear simply as diffused white 
spots. The marked difference between this imaging and that shown 
in Figure 24 (a) and (c) should be noted. 

It should also be noted here, that while in the imaging of point 
sources by the lens having substantially the same aberrations as the 
eye the images have characteristic forms and colored fringes due to 
their distances from the lens, in the imaging by the corrected lens, 
although there is a diffusion which may indicate that the point source 
is not in the object plane, there is nothing to indicate which side of the 
object plane it is or how far it is from it. 

In order to show the characteristic chromatic edges produced in the 
images of black and white objects, colored photographs of a black cross 
on a white background and of a white cross on a black background were 
taken with a lens having approximately the same chromatic aberration 
and oblique astigmatism as the eye, and also with a corrected lens. 
They are shown in Figures 25, 26, 27, 28, and 29. The photographs 
taken with the corrected lens will be considered first as they show the 
exact shape of the black and white crosses. 

Figure 28 was taken with a corrected lens of the crosses placed at C, 
Figure 23. The blue, yellow and red images are seen to be all of the 
same size and shape, the combined image will therefore be white and 
black with no chromatic edges. 

Figure 25 was taken with a lens having approximately the same 
chromatic aberration and astigmatism as the eye, of the crosses at C 
as in Figure 28. Being beyond both the primary and secondary 
astigmatic fields for blue the blue is generally diffused. Being in the 
secondary field for yellow the yellow horizontal or radial lines, both 
black and white, are relatively sharp, the vertical or tangential ones, 


oe AMES, PROCTOR AND AMES. 


diffused. Being nearer the primary than the secondary field for red, 
the vertical lines are sharper than the horizontal ones. The chro- 
matic edges that exist from the combined figures can be visualized by 
the amount the different colored edges extend in the different direc- 
tions. It is regretted again that these figures cannot be reproduced in 
color which shows the effects much more clearly. ‘The marked differ- 
ence in characteristic edges in this figure compared with Figure 28 is 
however plainly evident. 

Figure 29 was taken with the corrected lens of the crosses placed at 
B, Figure 23. A photograph of the crosses placed at D is so similar 
that it is not shown. 

Figures 26 and 27 were taken with a lens having approximately the 
same chromatic and astigmatic aberrations as the eye of the crosses 
placed at B and D, Figure 23. The characteristic diffusion and 
accentuation of vertical and horizontal lines for the different colors is 
evident and a little study will show that it takes place in conformity 
with the position of the primary and secondary object astigmatic fields 
for the different colors. 

The marked difference in characteristic imaging between these fig- 
ures and Figure 29 should be noted. 

In all these photographs the objects were at an angular obliquity of 
between eighteen and twenty degrees. If the angular obliquity had 
been less the characteristic imaging would be different due to the 
difference in the relative positions of the primary and secondary astig- 
matic object fields for the different colors. 


SUMMARY. 


The foregoing demonstrates that the retinal image of an object in 
space has characteristics both as to shape and colored edges due to the 
object’s particular position in space relative to the observer and his 
fixation point. In other words with a given fixation the image of a 
particular object in the field of view has characteristics which are 
peculiar to the image of an object at its particular angular obliquity 
and distance. 

That these characteristics are of sufficient magnitude to be recog- 
nized is evidenced by the fact that those doing research in this line 
have been able to discover and measure them. ‘The accentuation of 
radial and tangential lines is observable in landscape views. This 
accentuation can be observed in Figure 30. Hold up the page so that 
you can either look by its edge at some distant object or at the small 


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VISION AND THE TECHNIQUE OF ART. 23 


cross near the edge. If a distant object is focused the vertical line 
in the large cross is more evident than the horizontal line. If the 
little cross on the edge of the page is fixated the opposite is the case. 
Care must be taken not to let the accommodation or line of vision vary. 
These facts lead naturally to the assumption that with a given fixa- 
tion the characteristic imaging of oblique objects in space informs us of 
their distance; that is if an object has sharp tangential edges we judge 
it to be nearer than an object with soft tangential edges and if it has 
sharp radial edges we judge it to be farther away than an object with 
soft radial edges. If this is so, objects depicted in a picture with sharp 
tangential edges should appear nearer than those depicted with soft 
ones and objects depicted with sharp radial edges should appear 


Figure 30. Figure for observing change of appearance of radial and 
tangential lines with variation of focus. 


farther away than objects depicted with soft ones. This is exactly 
what was found to be the case as is shown by Figures 30a and 30b. 
Carefully observing 30a it will be seen that the circles with the sharp 
edges, whether inside or outside appear nearer than the circles with the 
soft edges. In Figure 30b it will be seen that the central portions of 
figure I which are sharp edged appear to be more distant than the 
circumference where the edges are soft, while in figure II where the 
radial edges near the center are soft and those near the outside sharp 
the center seems to be on the same plane as or nearer than the cir- 


cumference.® 


8 These illusions are more apparent if one eye is closed for the reasons given 
in the footnote page 15. 

The judgment of two hundred and two students at Dartmouth College were 
obtained on the effect of these illusions. On the figures in 30a 77.3% 
judged that the circles with the sharp edges appeared nearer than those with 
the soft ones. 19.8% made the opposite judgment and 2.9% got no effect. 

On the figures in 30b, I and II, 82.2% judged that the central portions of 
Fig. I appeared more concave than that in Fig. II. 17.8% made the opposite 


judgment. 


24 AMES, PROCTOR AND AMES. 


Figure 30a. Figures showing effect of depth produced by sharp and soft 
tangential edges. 


A 


VISION AND THE TECHNIQUE OF ART. 25 


4 4 1 | | | 


iy 


ap, 


Ris. 

—— => 
I 
II 


Figure 30b. Figures showing effect of depth produced by sharp and soft 
radial edges. 


26 AMES, PROCTOR AND AMES. 


In paintings made by Mrs. Oakes Ames in which objects on the sides 
of the pictures were depicted with these characteristics a marked sense 
of depth is given by the objects taking their proper relative distances. 
The accentuating of tangential and radial lines in their proper planes 
is found in many paintings, especially those of Turner in whose work it 
is apparent in the accentuation of tangential lines inside the focus and 
of radial lines on and behind the object plane of the scene he is painting. 
The accentuating of tangential lines in the foreground is found in many 
works of art and might be called almost a trick of composition to pro- 
duce an effect of depth. 

Although a large part of the above described effects are due to color 
and therefore cannot be reproduced in black and white, the photo- 
graphs in Figures 31 a and b taken with a lens having approximately 
the same oblique aberrations as the eye, and 32 a and b taken with a 
corrected lens, are shown to give an idea of the general differences 
obtained. The photographs in Figure 31 a and b are believed to give a 
greater effect of depth and to be generally more pleasing than those 
in Figure 32a and b.® 

The accentuation of the tangential lines and softening of the radial 
lines in the foreground are very apparent in the candle stick in Figure 
3la. The accentuation of the radial lines and the softening of the 
tangential lines in the background and plane of the focus are apparent 
in the books in Figure 31a and in the objects on the right and left of 
Figure 31b. 

The difference in the size of the books in Figures 3la and 32a is 
due to the distortion in Figure 3la. This distortion is approximately 
the same as existsin the eye. This difference in size may help to cause 
Figure 31a to give a greater sense of depth than Figure 32a. 


CHAPTER IV. 
DISTORTION. 


There is still another factor that affects the nature of the images of 
an object situated on one side of our line of vision. That is distortion. 
It can be defined as that characteristic of a lens which causes variation 
in distance between points in the image field which in the object field 
are equidistant. The eye is subject to so-called barrel distortion, 


9 It is regretted that the general loss of detail due to reproduction masks 
much of the effect which is apparent in the original photographs. 


Fig. 31b. 


Figure 3la and b. Views taken with lens having approximately the same 
aberrations and distortions as the eye. 


Fig. 32b. 


FicgureE 32a and b. Same views as in Figure 31 taken with a corrected lens. 


VISION AND THE TECHNIQUE OF ART. ot 


which means that a series of points subtending equal angles in space 
are not imaged at equal distances on the retina. ‘The images of equi- 
distant points at a distance from the axis are closer together than those 
near the axis, the farther from the axis the closer they are together. 
Figure 33 shows the approximate distortion which exists in the eye. 
If the eye looks at the center of a rectilinear grid, similar to the one in 
the figure, held at such a distance that when looking at its center the 
corner will subtend an angle of thirty-two degrees with the visual axis, 
the picture that is formed on the retina will not be a reproduction of 


Figure 33. Curves showing the ‘‘barrel’’ distortion of a rectilinear grid 
that takes place in the eye. 


the rectilinear grid but will take the form of the barrel shaped grid 
shown in Figure 33. By comparing the two grids it will be seen that 
points that are equidistant on the rectilinear, as shown by the inter- 
section of the cross lines, are not equidistant in the barrel shaped grid. 
They are practically the same distance apart near the axis but the 
farther away from the axis you go the smaller these distances become. 

The effect of this is twofold. It causes straight lines that do not 
pass through the axis of vision, to be bowed outward in their central 
portions. It also causes objects away from the axis to be imaged in 
smaller relative size than those near the axis. 


28 AMES, PROCTOR AND AMES. 


This effect applies to all objects depending in amount upon their 
angular obliquity regardless of their distance away. 

This distortion is very easily seen by looking at the middle of any 
rectilinearly bounded space such as the side of a room and, without 
allowing the axis of vision to change, noting the curvature of the bound- 
ary lines. 

It is in fact the most easily noticed of the characteristics of our 
retinal picture. 


SUMMARY. 


The effect of this distortion on the nature of the images of objects 
off the axis is very marked. It causes straight lines in a scene to be- 
come curved and take very different positions relative to each other 
from those laid down by the laws of disappearing perspective. At the 
same time it causes objects to one side of the line of vision to become 
relatively smaller. 

In corrected photographic lenses this distortion is corrected so that 
with such a lens a photograph of the rectilinear grid shown in Figure 33 
would also be rectilinear with all the squares the same shape and size. 
Figure 34, which is a photograph taken with a lens having the same 
distortion as the eye, shows the characteristic barrel distortion while 
Figure 35 shows the same scene taken with a corrected lens. The 
barrel distortion is shown in Figure 34 in the curvature of the lines in 
the tiling, of the edge of the tank and of the balcony. This distortion 
produces a more natural effect. This is most noticeable by comparing 
the ceilings in the two photographs. ‘That in Figure 34 seems to arch 
over properly, while that in Figure 35 flares upward. It is also evi- 
dent in the way the lower left hand corner of the tank is rendered. By 
comparison the corner in Figure 35 seems to fall away and gives the 
effect of the water not being level. 

It is of the greatest interest and significance, that of all the charac- 
teristics of the retinal picture distortion has been most commonly used 
by the great painters. That the “rectilinear” effect is not satisfactory 
has long been recognized. W.R. Ware in his book !° on perspective in 
a chapter entitled “ Cylindrical, Curvilinear or Panoramic Perspective” 
points out that the laws of ordinary disappearing perspective must be 
departed from in order that the depicting of certain features on the 
sides of the field of view shall appear satisfactory. He shows this is 
especially necessary in the case of certain architectural compositions, 


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VISION AND THE TECHNIQUE OF ART. 29 


and shows further many instances where this has been done by great 
artists. He shows further that satisfactory results can be gotten by 
introducing what practically amounts to a “barrel distortion.” It is 
not evident, however, that he recognizes the fundamental principles 
on which curved perspective is based. 

The writers have made what can hardly be called more than a casual 
search and has found distortion in the following works: 


Leonardo da Vinci “Last Supper” 
Puvis de Chevanne “St. Genevieve” 


Rembrandt Numerous instances 

Israels “The Day before Parting” ‘4 and “The Con- 
valescent”’ and other pictures 

Millet “Cliffs of Gouchy” }? 

Turner Numerous instances 

Whistler Etching Venice Scene, “The Palaces” First 
Venice Set 1880 

De Hoogh “Tnterior of a Dutch House” ! 

Van Vleet “Church Interior” } 

Inness “The Greenwood” 


The lack of its consistent use in most cases causes one to believe 
that those who used it did so intuitively to make the picture “look 
right.”’ Israels, however, used it so consistently that he probably was 
conscious of the law and the same is probably true of Rembrandt. 
The only example of it that has been found in the works of living 
artists is in Sir William Orpen’s painting “'The Peace Conference.” 
As only a photographic copy of this picture has been seen there is a 
possibility that the distortion was in the photograph. Figure 36 is a 
reproduction of Israels’s “The Day before Parting.” ‘The distortion 
is most evident in the tiling in the floor though it can be seen in various 
other parts of the picture. 

One would think that the representation of straight architectural 
features by a curved line coming next to the straight edge of the frame 
of the pictures as it often does would be very noticeable. It is not 
however. Not that it is not perfectly evident when one’s attention is 
called to it, but it does not attract one’s attention. Its evident effect 
in many cases is to prevent certain parts of the picture from looking 
as if they were falling out. 

In using distortion the detail, edges, etc., of the distorted features 


11 These pictures are at the Boston Art Museum. 


30 AMES, PROCTOR AND AMES. 


should be depicted approximately in the way they would be imaged on 
the retina. This was shown by the obtrusive unnatural appearance of 
a painting which Blanche Ames and Mr. Ames made in about 1912 
in which they put in the approximate distortion which exists in the eye 
but painted all the detail as it appeared while looking directly at it. 
In later pictures painted by Blanche Ames in which the detail of the 
distorted features approximated in its characteristics the way it is 
imaged upon the retina the distortion ceases to be noticeable and gives 
a pleasing and natural effect. 

Another interesting effect due to distortion results from the fact 
that objects away from the optical axis are imaged in smaller relative 
size than those near the axis. This effect is very evident in Figures 
31(a) and 32(a). In Figure 31(a) taken with the eye lens the statu- 
ette is much larger relative to the books than it is in Figure 32(a), 
although the statuette in both pictures is the same size. 

With a larger angular field this relative difference in size is still 
greater. In the eye where the field is between four and five times that 
in the figures the effect is very marked. This is probably the reason 
why a distant mountain appears so much larger to us when we look 
at it than it does in a photograph taken with a corrected lens. 


CHAPTER V. 


SENSITIVITY OF THE RETINA. 


As stated in the introduction, the character of the picture we get on 
the retina is determined not only by the kind of image that is formed 
by the lens system of the eye but also by the nature of the sensitive 
surface upon which the image falls, that is by the sensitivity of the 
retina. 

To gain a thorough knowledge of our retinal picture it is necessary 
therefore to know the sensitivity of the retina in its various parts both 
to light and to color. 

Unfortunately relatively very little is known as to the sensitivity of 
the retina as a whole. Considerable is known about the sensitivity of 
the fovea, i.e., that part of the retina which is on the axis of vision, but 
very little definite knowledge exists as to the sensitivity of the peri- 
pheral parts. 

A great deal of work has been done on the limits of the color fields, 
i.e., as to the limit of obliquity at which different colors are visible. 


VISION AND THE TECHNIQUE OF ART. aL 


The validity of that work, however, is put in question for reasons given 
in the article on “ Dioptrics of the Eye” !* by Dr. Proctor and Mr. 
Ames. 

As far as is known no quantitative measurements, with one exception 
which will be considered later, have been made of the color sensitivity 
of different parts of the retina. The late Dr. J. W. Baird and Mr. 
Ames undertook to make such measurements at Clark University in 
1913, but found that the aberrations of the lens system of the eye 
would first have to be determined. ‘This led to the work described in 
“Dioptrics of the Eye.’”’ Mr. Ames hopes to carry out these quanti- 
tative measurements later. 


68 2 16 2 @ 2 32 36 40 4 48 S2 SE GO C466 


Fieure 37. Curves showing sensitivity of the retina in various parts to 
light of different color. 


Dr. Baird and Mr. Ames did find that blue appeared much more 
saturated on the periphery than it did on the fovea. This is in con- 
formity with measurements made by Abney.‘? He measured the 
sensitivity of the retina to lights of different wave lengths both at the 
fovea and at an angle of ten degrees. His results are shown in Figure 
37. It will be seen that blue appears brighter at ten degrees than at 


12 Loco Set. 
13 ‘Researches in Color Vision,” p. 94, Longmans Green & Co., 1913. 


oD AMES, PROCTOR AND AMES. 


the fovea. The amount brighter that blue light of different wave 
length appears is shown in Figure 38. 

This greater peripheral intensity of blue is probably primarily due 
not so much to the difference in sensitivity of the retina in the two 
regions as to the absorption of blue light at the fovea by the yellow 
spot. The yellow spot lies over the fovea, covering an angular area of 
about six degrees horizontally and four vertically. Its effect is to 
absorb light of short wave lengths, 1.e., blue. 

The effect on our retinal picture of this difference in sensitivity is to 
cause those parts which are outside the yellow spot to appear more 


"Ralie eis 
Sensitiveness of the Retine 
10°. from Tovea To 
that of yetes Spot near the 


ovda. 


Figure 38. Curve showing ratio of sensitivity of the retina 10° from the 
fovea to that at the fovea. 


blue. This effect was very evident to Dr. Proctor and Mr. Ames 
while measuring the astigmatic fields for blue light, the blue light ap- 
pearing many times brighter when it was a few degrees off the axis 
than when looked at directly. The sensation is also commonly experi- 
enced in the falling off of the apparent blueness of something one sees 
out of the side of the eye when one turns to observe it directly. | 

To approximate this effect photographically a yellow spot of approx- 
imately the proper absorption and of about six degrees in angular size 
was put in the middle of the blue focal plane filter which with a red and 
green filter was used to take three color photographs. ‘The exposure 


—_——_«.* 


VISION AND THE TECHNIQUE OF ART. 33 


for blue was then made sufficiently longer so that the color rendering 
would be normal in the center of the picture while on the outer parts 
the blue would be stronger in approximate accordance with the results 
found by Abney. A lens having the approximate aberrations and 
distortion of the eye was used. 

The results were very interesting. The effect was two-fold; first: 
to render all the colors outside of the “yellow spot” bluer; second: 
to make more apparent the aberrations in the images formed by oblique 
rays and thus cause a greater softening of the outer parts of the picture. 
In the photographs in which the color rendering all over the picture 
was the same as we get in our yellow spot the aberrations of light 
from the blue end of the spectrum, although they existed, were.so low 
in intensity as to produce no effect. When, however, the intensity of 
the blue light was made greater these aberrations became apparent. 

These effects are primarily chromatic and show very poorly in black 
and white reproductions. The difference in the apparent aberration 
however is evident in the photographs shown in Figures 39a, b, and c. 
These were taken with a lens having the approximate aberrations of 
the eye. In Figure 39 (a) no filter used. In Figure 39 (b) a filter 
having the approximate absorption of our yellow spot covered the 
entire picture. In Figure 39 (c), which represents the conditions we 
get in our eye, a similar filter covered an angular area corresponding to 
that of the yellow spot. 

It will be seen that the whole of the picture in Figure 39 (a) is much 
softer than that in 39 (b). This is due to the greater amount of the 
aberrated blue light which struck the plate in Figure 39 (a) and which 
is absorbed by the filter used in taking 39 (b). In Figure 39 (c) the 
center portions are sharp due to the local action of the yellow filter 
while the outer part is soft due to its absence. It is very evident that 
Figure 39 (c) which approximates the conditions we get on our retina 
is much more pleasing !4 than Figure 39 (a) or 39 (b). Figure 39 (d) 
is a photograph of the same scene taken with a corrected lens. This 
seems to be pretty conclusive evidence that the purpose of the yellow 
spot is to counteract the strong chromatic aberration in the eye by 
reducing the brightness of the light from the blue end of the spectrum 
so that it ceases to be apparent. 


14 It is regretted that a very marked effect that is apparent in the original 
photograph is lost in the reproductions. 


a4 AMES, PROCTOR AND AMES. 


SUMMARY. 


The above facts show the marked effect that variations in sensitivity 
of the retina have on the nature of our retinal picture. 

The slightly brighter warmer centers in some of Corot’s pictures 
suggest the effect produced by the yellow spot. But besides his work 
the only evidence that has been found that the above described effects 
have been made use of by artists is in their very common practice of 
rendering shadows in out-of-door scenes much bluer than they appear 
when one looks directly at them. As far as is known this has not been 
limited to the outer parts of their pictures. The blue appearance of 
shadows which are imaged on the side of the retina are, however, very 
easily seen, and as this effect holds true over the greater part of the field 
of vision it was probably found that pictures look better with blue 
shadows all over them than without any blue shadows at all. 

As has been stated our knowledge of the sensitivity of the retina is 
very limited. We already know, however, that our capacity to dis- 
tinguish detail away from the center of focus is largely due to the 
structure of the retina. It is probable that a further knowledge would 
give suggestions as to the laws which control the difference of local 
values of which we are conscious on the different parts of the retina. 

There are also of course other effects such as contrast, simultaneous 
and successive, and after images which must have a marked influence 
on our retinal picture. ‘Their use in pictures raises the thought of the 
possibility of suggesting eye motion. 


CHAPTER VI. 
BINOCULAR VISION. 


The fundamental idea in undertaking the research work which is 
the basis of this article was that pictorial art should be similar to our 
mental visual images, and, since our mental visual images are probably 
similar to our retinal pictures, valuable suggestions could be obtained 
from a knowledge of the characteristics of our retinal picture. Our 
mental visual impression, however, is not derived from a single retinal 
picture but from two, as we normally look with two eyes. . 

The whole subject of binocular vision is too long and complicated to 
be considered here. It was believed, however, that some of the char- 
acteristics of binocular vision under particular conditions could be 
reproduced in a single picture such as a photograph or painting. 


age 


Figure 39a. View taken with a lens having the same chromatic aberration 
as the eye. 


FicgurE 389b. Same view as in 39a taken with lens having the same chro- 
matic aberration as the eye and a focal plane filter having the approximate 
absorption of the ‘yellow spot” covering the whole picture. 


FicgureE 39c. Sameas39b. The focal plane filter covering the area covered 
by yellow spot thus approximating the conditions we get in one eye. 


Figure 39d. Same view taken with a corrected lens and no filter. 


‘ydvisojoyd ,.cv]no0UuUOW,, [F PINS UI SY MOA OUIVG “ZH AUMNYIT 
‘ydeisojoyd ,.avynooulg,, ‘“[Pp @uadIy 


"SP “SL 


VISION AND THE TECHNIQUE OF ART. 35 


The conditions chosen were where the background behind the object 
at the point of convergence was of an indeterminate nature such as a 
mass of branches or foliage. The absence of any marked contours 
under such conditions would not call for the suppression of parts of 
either retinal image. 

Leaving out the effect of ocular movement and the fusion of doubled 
images the brain under such conditions may be considered as receiving 
two superimposed pictures of the object field as seen from each eye. 

To reproduce this effect a camera was devised which, by means of a 
reflector and half silvered prism, produced superimposed pictures of the 
landscape as viewed from two points of view,— the distance between 
which was the same as that between the eyes. The detail in these | 
pictures superimposed where the axis of the two systems crossed, as 
the two monocular images do at the point of convergence. The de- 
tails in all other parts of the pictures were more or less doubled due 
to the parallax of the two systems. 

Figure 41 shows such a “binocular” photograph. Figure 42 shows 
an ordinary photograph of the same scene. 

The following characteristics will be noted in the “binocular” 
picture: 

First, there is a “broadening” of everything in a horizontal direc- 
tion. At the convergence point this is due to seeing more of the sides 
of an object. At other points in the scene it is due to the doubling in a 
horizontal direction resulting from the parallax. This effect of the 
“broadening” of a scene when viewed binocularly can be noticed by 
anyone by first observing the scene with one eye and then with two. 

Second, there is an increase in contrast values between the lights 
and darks in the objects at the convergence point relative to that in 
other parts of the picture. This is due to the fact that at the con- 
vergence point the darks and lights superimpose and so reinforce each 
other while in all other parts of the picture they tend not to superim- 
pose and so counteract each other. Probably some such effect as this 
exists in our binocular impression. | 

Third, there is a doubling up of the images of objects not at the 
convergence point, the extent of the separation of the doubled images 
depending upon their distance from that point. The seeing of objects 
not at the convergence point in doubled images is supposed to be one 
of the factors that gives us our idea of relief, the extent of the doubling 
suggesting the distance of the object from the convergence point. The 
impression we receive on our mind from these doubled images is differ- 
ent from that shown in Figure 41 due to the modifying effects of the 


36 AMES, PROCTOR AND AMES. 


antagonism of the visual fields which suppresses one set of images, and 
to other physiological factors. Our impression, however, is probably 
more like the effects shown in Figure 41 than like a monocular impres- 
sion, as is shown by the greater effect of depth, less flat appearance of 

Figure 41 as compared with Figure 42. 


SUMMARY. 


It is well known among artists that a different effect is produced 
from painting with one eye than with two and that to get satisfactory 
results two eyes must be used. There are unquestionably certain 
effects in the binocular impression that can be reproduced in a single 
photograph and still further effects that can be reproduced in a paint- 
ing, where factors such as antagonism of the visual fields can be dealt 
with. There are other effects due to ocular movements which cannot 
be reproduced in a single picture but which may be possible of repro- 
duction in motion pictures. 


CuHaPTer VII. 


GENERAL SUMMARY AND DISCUSSION OF RESULTS. 


From the foregoing description of the characteristics of retinal 
images of objects in various parts of the visual field it is possible to 
determine fairly definitely the nature of the retinal picture as a whole. 
It can be described, in general terms, as being a picture in which ob- 
jects at the center of interest, or focus point, are depicted in consider- 
able detail, but not with microscopic detail. 

Objects in the field of view, nearer or farther from the observer than 
the center of interest, are depicted with less detail and with chromatic 
edges the color of which depends upon the position of the objects 
relative to the center of interest. 

Objects lying to one side of the line of vision are also less clearly 
depicted, the lack of clearness increasing with the angle of obliquity, 
the accentuation of detail and edges in such objects depending upon 
their position relative to the center of interest. Speaking generally 
this accentuation is in a tangential direction if the objects are situated 
nearer to the observer than the center of interest and in a radial direc- 
tion if they are on the plane with or behind it. Such oblique objects 
also have characteristic chromatic edges depending upon their position 
relative to the center of interest. 


VISION AND THE TECHNIQUE OF ART. 37 


All oblique objects are distorted and changed in shape varying in 
amount with their obliquity. ‘This distortion is shown in the bowing 
out in their central portions of straight lines which do not pass through 
the center of interest and a reduction in size of oblique objects. 

And finally the color of the picture in its outer parts is bluer than at 
its center. 

In our ordinary habit of vision, when looking at a scene, we focus on 
some particular part or object in it due to its special interest or beauty 
to us; we hold that focus for a moment or two and then look at 
another center of interest or another or look away entirely. With 
each fixation of the eye a retinal picture of the kind just described is 
formed. We therefore receive on our retinas a series of such pictures. 


MENTAL VISUAL IMAGES. 


The question arises: What is the nature of the mental visual images 
which we have of actuality? Without doubt, our brain receives a 
series of impressions similar in character to our retinal pictures. But 
how are those impressions registered in our consciousness and memory. 
There are two general possibilities. One that our visual memory 
consists of a series of pictures similar in nature to our retinal pictures. 
The other that, by some mental process, these serial impressions are 
combined and form a memory impression similar to actuality as we 
know it exists intellectually, i.e., with the detail all over the picture 
sharp and clear and with no colored edges or distortion. 

Although there is no known psychological work on the analysis of 
mental visual images to substantiate the conclusion, what evidence 
there is indicates that our mental visual images consist of a series of 
images similar to our retinal pictures. This was the opinion of the 
well known psychologist, Dr. J. W. Baird, who mentioned as a reason 
for such belief the relatively definite character of the center and 
nebulous character of the outer parts of our mental visual images both 
when we are awake and when we are dreaming. Such a view is further 
substantiated by the fact that the indefiniteness in those parts of a 
scene that are not at the focus point and other characteristics of our 
retinal picture give a sense of depth and relief. A sacrifice of these 
characteristics would mean a sacrifice of effect of depth in our mental 
visual images which would seem most improbable. 

Furthermore the existence of a mental visual image of a scene similar 
in detail to the scene itself could only be based on a visual knowledge 
of all the detail in the scene. This could only be acquired by passing 


38 AMES, PROCTOR AND AMES. 


the fovea or clear seeing part of the eye over every part of the scene 
which of course, is never done in the ordinary habits of vision. It also ° 
assumes some process of mental synthesis of particular parts of a series 
of impressions; of the existence of such a process we have no evidence. 

It is believed that it can be concluded that our mental visual images 
of actuality consist of a series of images similar in general character to 
the picture we receive on our retina, or more accurately a series of com- 
bined pictures such as we receive on our two retinas. 


METHODS OF DEPICTING NATURE. 


In the arts, painting, drawing, sculpture, photography, our purpose 
is to depict nature. There are in general two ways in which this can 
be done. 

First, a reproduction of the actuality can be attempted. By this is - 
meant as close a reproduction as possible of all the objects in the scene 
in every measurement and detail. In sculpture the well known wax 
figures do this most successfully, though much work in marble and 
clay does so very closely. In the pictorial arts it has been most closely 
approximated by photographs taken with a corrected lens. Many 
paintings in which all objects have been depicted in full detail, as they 
appear on the fovea of the eye when directly observed, also very closely 
approximate actuality. By this is meant that the objects are so placed 
in the picture and the details of the objects are so depicted that, if the 
picture is viewed from the proper distance, all the objects will lie in 
the same angular direction as they do in the scene itself; while the 
depicting of each object is such as to produce to the eye looking directly 
at it the same appearance that the object itself would produce were the 
eye looking directly at it. 

In a photograph this is accomplished by using a corrected lens; that 
is, one which has been so designed and constructed that every object 
in the field is imaged with as great detail as possible and the images of 
objects in the image plane have the same relative lateral positions to 
each other as the objects themselves. The same result is accomplished 
in a painting or drawing in which the artist depicts every part of the 
scene as it appears to him while looking directly at it. Every object 
will then be represented in full detail whether near, far, or on one side 
of the field of view, and the depicted objects will lie in the same relative 
lateral positions to each other as the objects themselves. 

While such representations of nature are a reproduction of actuality 
in the accuracy with which the detail and relative lateral positions of 


VISION AND THE TECHNIQUE OF ART. 39 


objects are depicted, they do not reproduce the positioning of objects 
situated at different distances. This is impossible because a picture is, 
of necessity, on a flat surface where everything depicted must be the 
same distance from the observer, whereas nature exists in tri-dimen- 
sional space.® Due to this fact, the picture as a whole can never give 
the same effect to one looking at it as one gets from looking at nature. 
For in looking at one part of a natural scene, objects at all other dis- 
tances take on characteristic appearances due to their different dis- 
tances. In a picture where they are all reduced to one plane this is 
not true. i 

The second way in which the depicting of nature can be attempted 
is, instead of trying to reproduce actuality itself, to attempt to repro- 
duce the impression that nature makes on the human consciousness, 
i.e., to reproduce mental visual images. The general characteristics 
of our mental visual images are, as it is believed it has been shown, 
similar to those of the retinal pictures. 

Such depicting of nature can be approximated photographically by 
means of a lens which produces the same characteristic imaging as the 
lens system of the eye, and a plate whose sensitivity over its various 
parts is similar to that of the retina. It can be approximated in paint- 
ings and drawings if the artist keeps focused on whatever he picks out 
as the center of interest and depicts everything else as it appears to 
him while keeping his eye focused on that point. Artists who have 
very clear and lasting mental visual images closely approximate it by 
copying those images directly without regard to actuality. 

As the retinal picture lies on a surface and as the canvas or paper 
on which it is depicted is also a plane surface, there does not seem to 
be the same fundamental limitations in reproducing it that exists in 
attempting to reproduce tri-dimensional actuality. In reproducing 
the subjective binocular impression in a single picture there do exist, 
however, the limitations which arise from the impossibility of repro- 
ducing those parts of the impression which we get from eye movement 
and motor impulses. 

For all artistic purposes, it is believed that the attempt should be to 
reproduce not the actuality but the impression which it makes on us. 
Three general facts may be given in support of this. 

First, the use by so many of the great painters of characteristics of 
the retinal picture which is the strongest evidence of the artistic value 


15 Stereoscopic photographs do reproduce the effect of the third dimension. 
They are not however satisfactory from an artistic point of view, and as we are 
dealing only with single pictures will not be considered here. 


40 AMES, PROCTOR AND AMES. 


of pictures of this type. Second, photographs taken with a lens which 
approximately reproduces the characteristics of the retinal picture 
are more pleasing than those taken with a corrected lens. Third, 
photographs taken with corrected lenses are the most perfect repro- 
duction of actuality which we have, much more accurate than can 
probably ever be accomplished with brush or pencil, yet this type of 
picture is admittedly a complete failure from an artistic point of view, 
indeed its failure seems to be due to the fact that it does reproduce 
actuality so accurately. 

The following three argumentative reasons are also given: 

First, the general accepted belief that artistic expressions are sub- 
jective. The purpose of the great artist is to make others see nature 
as he sees it. He could convey no more by reproducing actuality to 
those who look at his picture than they would get by looking at the 
scene itself. He has to put into his picture nature’s impression on 
himself, the beauty and the truth he sees. Second, the subtle varia- 
tions and differences which cause him to see the scene beautifully are 
alterations in his mental visual images due to personal psychological 
factors. The depicting of such subtle differences could be much more 
easily accomplished in a picture which in its general type was similar 
to his subjective impression than one which was not. Third, the 
purpose of art is to awaken subjective associative processes in those 
who look at it. This is especially evident in portraiture. The natural 
way to cause us to recall our mental visual images or start a train of 
them in motion is to present to us a picture similar to them. 

When we look at a picture of this type we recognize that it is an 
attempt to reproduce not actuality but our impression of actuality. 
Where we see the objects farther away than the object in focus depicted 
without much detail we do not think that they in fact did not have 
detail in them or perhaps that an intervening mist existed which 
obscured the detail but we know that such objects were farther away 
than the object in focus. And similarly with the distortion of line on 
the side of the field of view, we do not think that a building, for 
instance, so depicted is in fact curved. We recognize that such is the 
character of our subjective impression of a building on one side of our 
field of view. ‘That is we pass our fovea or the part of our eye that 
gives us distinct vision over the picture and recognize its various parts 
as being similar to our mental visual image, just as we can direct our 
attention to various parts of such an image. 

There is possibly a third way to attempt to depict nature, which 
may be considered a modification of the first method above described. 


VISION AND THE TECHNIQUE OF ART. 41 


In such a picture, all objects not at the center of interest would be 
painted so that, when the center of interest in the picture was looked 
at, the picture as a whole would make an impression similar to that 
produced by the scene itself. Such pictures as photographs taken with 
corrected lenses attempt to do this but, as has been stated, fail in that 
they do not give a proper suggestion of depth. 

In this third type this deficiency might be met by accentuating the 
characteristic imaging of all objects not at the focus point to suggest 
their position in tri-dimensional space. For instance, near dark 
objects, in the line of focus, would be shown with red edges, distant 
ones with blue; and, on the sides of the picture, the radial accentuation 
of distant objects and the tangential accentuation of near objects 
would be shown. 

In making these peripheral accentuations it would have to be borne 
in mind that they would be modified by the oblique aberrations of the 
eye as they would lie on the peripheral part of the picture and be 
imaged on the periphery of the retina. Allowances would therefore 
have to be made. As the picture plane lies near the secondary 
astigmatic field the radial accentuations would have to be relatively 
slight and tangential accentuations relatively marked. No distortion 
would be put in such a picture as the eye itself would introduce it, if 
the picture was viewed from the proper distance. 

Granting that the proper accentuation of the radial and tangential 
and chromatic edges could be made, which would be very difficult, it is 
questioned whether such a picture would be satisfactory. 

The proper impression could only be produced when the center of 
interest of the picture was looked at. If any other part of the picture 
was looked at that part would not only appear like nothing ever seen 
before but the rest of the picture would then cease to produce the 
proper impression. 


THE RETINAL PICTURES AND ARTISTIC PHOTOGRAPHY. 


As has been stated cameras in their inception were copied after the 
eye. It can be argued that the value of photographs for pictorial 
purposes rests on two quite different bases. One that it lies in repro- 
ducing in black and white, or in photographs in color, the same general 
picture we get on our retina. The other that it lies in reproducing in 
light and shade detail and color the effects that exist in nature. 

On the first basis it can be said that the results, when looked at, are 
satisfactory because they appear to us similar to the impression we 


42 AMES, PROCTOR AND AMES. 


have received. On the second basis it can be said they are satis- 
factory because in looking at them our eye is affected in the same way 
as it is affected by nature. 

In spite of the inherent impossibility already pointed out that the 
effect of objects in tridimensional space cannot be reproduced on a 
flat surface, it seems to have been the second basis that was followed 
in the evolution of the art of photography. This led to the develop- 
ment of corrected lenses which would image everything in the field of 
view in full detail with no distortion. 

After such lenses had been perfected it was found that the photo- 
graphs taken with them, although having unquestioned value for 
scientific and other purposes, were not satisfactory from an artistic 
point of view. 

Then followed the use of so called “soft focus” lenses, and various 
manipulations in printing and enlarging to get away from the hard full 
detail effect produced by corrected lenses. ‘Those desiring artistic 
effects bought up old lenses such as were used in making daguerreo- 
types and had lenses designed in which various aberrations were left 
uncorrected. As a result there has of late years been a most marked 
advance in the artistic side of photography, 

The method of development has however been one of “cut and try” 
and as far as is known, with the exception of the work done by Gleichen 
mentioned above, no fundamental laws have been followed. In- 
numerable methods and lenses have been tried and only those pro- 
ducing pleasing effects have survived. 

It is believed that the advance in artistic effect has been due to the 
fact that the results obtained were more similar to the subjective im- 
pression and that future developments in photography on the artistic 
side will come from approximating as closely as possible the retinal 
pictures and mental visual images. 


THE RETINAL PICTURES AS THE BASIS OF THE TECHNIQUE 
OF ART. 


In the chapters describing the characteristics of retinal images of 
objects situated in different parts of the field of view examples were 
given of paintings by artists in which these characteristics appear. 
The lists do not mention a far greater number of works that are in 
general suggestive of the retinal picture without showing the special 
characteristics noted. Of these Corot is the best example. Whistler, 
Manchini and Abbot Thayer and many others are also examples. 


VISION AND THE TECHNIQUE OF ART. 43 


This similarity to the retinal picture is shown in a tendency to accentu- 
ate the center of interest and lose detail elsewhere. This is especially 
evident in black and white work and in etchings. An explanation of 
this may be that it is easier to accomplish in black and white work. 
For in that part of the picture where it is desired to lose detail, detail 
is simply left out, the white paper suggesting blankness. Where color 
is used this cannot be done. Some color must be put on-the canvas 
and then the difficulty arises of getting on the right colors in the right 
way. 

It is believed that anyone going through a gallery, with the points 
of views here set forth in mind, will be impressed by the fact that the 
works of many of the best men show a suppression of detail in those 
parts of the pictures which are not the center of interest. And there 
will not be the slightest question that, in most cases, the entire picture 
is not painted as it would appear if every part of the scene were 
looked at directly. 

It is also very interesting to note that it is almost a general rule that 
the early work of most of the great masters was, so to speak, tight and 
hard, photographic. There is a very good example of this in an early 
picture by Corot in the Boston Art Museum. Later their style or 
technique changes. Their work is done more’ broadly especially the 
outer parts and their pictures get a center of focus and, to use a stock 
term, compose. 

It cannot be questioned that the change is a departure from a 
photographic reproduction of the scene. But the question may still 
remain: what are the laws that govern this change in style or tech- 
nique? ‘The commonly accepted belief is that, if there are any laws, 
they are purely aesthetie or psychical, and that the artist puts in and 
leaves out and changes solely according to the dictates of his personal 
taste. In view of what has been shown, especially the use by so many 
great painters of distortion, see Chapter IV, it is believed that the 
improvement in technique of these artists was due to a development of 
their vision. Consciously or unconsciously they approximated the 
scene as it would have appeared to them had they kept their focus 
upon the center of interest. i 

The difficulty which arises in this method of painting is to know how 
to reproduce the impression that one gets from an object at which one 
is not looking. That the capacity to recognize and analyze such 
impressions can be developed is shown by fact that some of the char- 
acteristics of such impressions have been represented by numerous 
artists. That this is very difficult is shown by the fact with all the 


44 AMES, PROCTOR AND AMES. 


genius we must attribute to the great artists, there is, it is believed, no 
artist who has intuitively recognized and depicted all the character- 
istics above mentioned; and in spite of the fact that distortion, the 
most apparent of these characteristics, has in the past been used by 
many great artists it has been recognized and used as far as the writers 
know by but one artist living today, i.e., Sir William Orpen. 

In fact so little do we know as to what we see that the ordinary 
person, including art students and many painters, do not know that 
we see clearly only those objects upon which we focus. They believe 
that the whole of the field of view is clear because when they are inter- 
ested in the question of the clarity of any part of it they look directly 
at it and are unconscious of the eye movement. 

Granting that it is desirable for the painter to be able to recognize 
and depict the character of his retinal impression it is believed that 
there is no question but that he can be greatly helped by an intellectual 
knowledge of the characteristics of his retinal picture. The knowledge 
that he never sees the whole of the scene with equal clearness will, 
after he has tried a few times, awaken his consciousness to the fact 
that he sees objects away from the center of focus less clearly. The 
knowledge that the characteristic edges and shapes of those objects — 
not at the center of interest can be seen only if the eye is kept focused 
on the center of interest will enable him to see these characteristics. 
The knowledge of distortion and the perception following therefrom 
will cause him to become conscious of its existence. Similarly the 
knowledge of the characteristic chromatic edges of objects nearer and 
farther than the focus point, of the accentuation of radial and tangen- 
tial lines and of the greater brightness of blue at a slight obliquity 
will lead to his conscious perception of these phenomena. Apart from 
the matter of developing his perceptions, the knowledge of the char- 
acteristic imaging of objects in various parts of the field of view will 
enable him to produce an effect of depth without the use of, or to 
supplement, the means now used. It will also enable him to produce 
a natural center of interest. 

The objection has been raised that such an intellectual knowledge 
would be harmful to an artist by destroying the “innocence” of his 
eye. That is in his knowledge of and expectation of seeing these 
things, he would see them where they do not exist, or would over- 
accentuate them. If the eye were “innocent”’ in the first place such 
an objection might have weight. But it is not. Take for instance 
the matter of the detail which we see in objects. We know that all 
objects both those in focus and those nearer and farther are sharp and 


VISION AND THE TECHNIQUE OF ART. 45 


clear, so we think we see them sharp and clear while in fact we see the 
objects out of focus with fuzzy edges. 

And likewise in the matter of distortion. We know that the side of a 
building is straight. That knowledge destroys the innocence of our 
vision and makes us think we see it straight out the side of our eye 
when in fact we see it curved. “Innocence” is already gone. To 
restore truth to the eye, we have to learn that under certain conditions 
we see chromatic edges on objects which are in fact sharp and curved 
lines in place of straight ones. The same line of argument applies to 
the other characteristics of the retinal pictures. 

The development of art seems to have been a struggle to put down 
what we see and not what we know or think we see. The Egyptians 
for instance in drawing an eye as seen from in front on a face in profile 
were putting down not what they saw but what they knew. So they 
put in the same picture what they saw from two different points of 
view. We are confident that today we paint things as we see them. 
But on consideration are we not making just as bad a mistake when we 
paint an object in the foreground and one in the distance with equal 
clarity, or when we paint straight lines on the side of the picture 
straight. It is just as impossible for us to see both near and distant 
objects equally sharp at the same time or to see straight lines on the 
side of our field of view as straight, as it was for the Egyptian to see the 
eye from the front view in the face from the side view. 

The conclusion must be that the “innocence”’ of vision can be 
developed by intellectual suggestions. Such suggestions which help 
the artist to know what he sees will also bring within the grasp of his 
intellectual consciousness, so that he can definitely perceive it, what 
formerly he could only feel intuitively and will leave his intuition free 
to reach out for the subtler expression of truth and beauty. 

In the ultimate analysis what the great artist expresses through his 
work is a matter of his own mental and spiritual visual images of 
beauty and truth. Their character depends upon his personality and 
psychology. Of necessity these factors will modify the character- 
istics of his retinal pictures, to what extent it is impossible of course to 
say. Itis believed however that the technical structure of his work is 
based upon his retinal impressions. The similarity of his retinal image 
to those of the rest of mankind will insure a universality of understand- 
ing and appreciation. 

It should be clearly understood that it is not suggested that the 
methods of depicting the various parts of a scene which have been 
described will in themselves make a great work of art. They are 


46 AMES, PROCTOR AND AMES. 


simply matters of technique, the grammar so to speak of the expres- 
sion. The quality that makes a great work of art is what the artist 
expresses through his work. Masterpieces expressing great truth and ~ 
beauties have been done with entirely different bases of technique, 
the work of the “ Primitives” as compared with that of the Barbizon 
School, for instance. Genius will express itself through any technique, 
but certain techniques will give greater possibilities for depth and 
subtlety of expression than others just as a modern piano, or violin or 
full orchestra gives the musical composer more freedom than the 
shepherd’s pipes. 

It is believed that everything that has been said applies to scuplture 
as well as to painting, taking into consideration of course that sculp- 
ture is tridimensional. 

Its usefulness in architectural drawings seems to be pretty conclu- 
sively proved by Figures 34 and 35. As to its application to archi- 
tecture itself, the writers do not feel qualified to speak. The belief 
that it is applicable can only be based on the assumption that in 
architecture we desire a subjective impression of a preconceived recti- 
linear arrangement. It would seem that under certain circumstances 
this might be desirable. The possibility immediately comes to one’s 
mind that there may be a connection between the curves in Greek and 
Gothic architecture and the characteristics of our retinal image. 

Before closing it might be interesting to suggest a line of thought to 
which the determination of the more specific characteristics of our 
retinal pictures might lead. In the first_place the characteristics of 
our retinal pictures are greatly affected by external physical condi- 
tions. ‘Take for instance retinal pictures of a scene in the day time and 
at night. Due to the enlarged pupil with which the night scene would 
be viewed and the greater sensitivity of the retina to blue light, as 
shown by the left hand curve in Figure 37, the characteristics of our 
retinal picture of the night scene will be very different from those of 
the day scene. It is believed that there is no doubt that pictures 
depicting these characteristics would most strongly suggest the external 
physical conditions which give rise to them. Further, the eye is a 
most delicately sensitive organ and is without doubt, affected by our 
bodily and likewise by our grosser emotional states. It is conceivable 
that the characteristics of our retinal pictures are also affected, and 
that specific bodily and emotional states are accompanied by specific 
changes in the characteristics of our retinal pictures. This in turn 
opens up the possibility that if the characteristics produced by a 
particular bodily or emotional state were depicted in a picture, the 
picture would suggest that particular state to those looking at it. 


VISION AND THE TECHNIQUE OF ART. 47 


CONCLUSIONS. 


1. Every object in space is imaged on the retina with character- 
istics of form, color, accentuation of line and chromatic edges, due 
to its particular position relative to the focus point. 

2. ‘These characteristics, of which the observer may or may not 
be conscious, suggest to him the position of the object in space relative 
to his fixation point. 

3. The reproduction in a picture of these characteristics of images 
of objects causes the depicted objects to appear in the same relative 
positions that they occupied in space. 

4. A pictorial representation of nature to be technically satisfactory 
from an artistic point of view should be similar to our subjective 
impression. It should not attempt to reproduce actuality. 

5. Our subjective impressions are, in their general character, simi- 
lar to the pictures we receive on our retinas while holding one center 
of focus. 

6. A pictorial representation of nature to be technically satis- 
factory from an artistic point of view should be similar in its general 
characteristics to the pictures we receive on our retinas while holding 
one center of focus. 

7. An intellectual knowledge of the characteristics of the retinal 
image of objects not at the center of focus helps one to become visually 
conscious of such characteristics. 


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